Kuhn E M, Therman E, Susman B
Department of Biostatistics and Epidemiology, Medical College of Wisconsin, Milwaukee 53226.
Placenta. 1991 May-Jun;12(3):251-61. doi: 10.1016/0143-4004(91)90006-2.
The possible occurrence of amitosis has been studied in nuclei of trophoblast outgrowths of mouse embryos placed in culture at the two-cell stage. By day 7 of culture, the inner cell mass has usually floated away, while the trophoblast outgrowth remains attached. Of 591 trophoblast cells from 25 embryos, 469 were uninucleate, 87 binucleate, 4 trinucleate, and in 31 the nuclei were attached to each other. In our interpretation, these come about through a process in which the nucleus stretches, then the nuclear membrane invaginates and finally constricts the nucleus into two parts. The resulting nuclei, asymmetric in size and in amount and arrangement of heterochromatin and nucleoli, lie side-by-side. We conclude that these cells with two or more attached or separate nuclei represent stages in true amitosis. In Table 1, amitosis is compared with mitosis without cytokinesis and with cell fusion, both of which can also give rise to binucleate and multinucleate cells. Mitosis without cytokinesis does not agree in any respect with the characteristics of amitosis, whereas at least a few similarities exist between cell fusion and amitosis. However, amitosis may give rise to near-haploid nuclei, which cannot be produced by mitosis or cell fusion. Simultaneously with amitosis, the nuclei grow through endocycles. In many nuclei, the heterochromatin is clearly underreplicated, while the nucleoli are numerous and often of enormous size, probably reflecting amplification of the rRNA genes.
已对处于二细胞期培养的小鼠胚胎滋养层细胞生长物的细胞核中可能发生的无丝分裂进行了研究。培养至第7天时，内细胞团通常已漂浮离去，而滋养层细胞生长物仍附着着。在来自25个胚胎的591个滋养层细胞中，469个为单核，87个为双核，4个为三核，31个细胞核相互附着。我们的解释是，这些是通过一个过程形成的，即细胞核先伸展，然后核膜内陷，最后将细胞核缢缩成两部分。由此产生的细胞核大小不对称，异染色质和核仁的数量及排列也不对称，它们并列存在。我们得出结论，这些具有两个或更多附着或分离细胞核的细胞代表了真正无丝分裂的阶段。在表1中，将无丝分裂与没有胞质分裂的有丝分裂以及细胞融合进行了比较，后两者也可产生双核和多核细胞。没有胞质分裂的有丝分裂在任何方面都与无丝分裂的特征不一致，而细胞融合与无丝分裂之间至少存在一些相似之处。然而，无丝分裂可能会产生近单倍体细胞核，这是有丝分裂或细胞融合所不能产生的。在无丝分裂的同时，细胞核通过内循环生长。在许多细胞核中，异染色质明显复制不足，而核仁众多且往往非常大，这可能反映了rRNA基因的扩增。
